Using nonlinear mixed effects models to estimate size-age relationships for black bears

Size-age relationships for three physical characteristics, body length, zyg omatic width, and pad width, were modeled for black bears (Ursus americanus ) captured in northeastern Minnesota, U.S.A. Because the curves representin g size-age relationships were nonlinear, and because some of the data consi st of repeated, longitudinal observations for multiple bears, nonlinear mix ed effects model analyses were required. The results are presented as param eter estimates with standard errors and estimated population curves with 95 % confidence intervals. Variance estimates obtained using mixed-effects mod els are compared with erroneous estimates obtained using ordinary least-squ ares techniques. Comparisons are made between male and female Minnesota bea rs with respect to parameter estimates and estimated population curves. In addition, the results for Minnesota bears are compared with results from si milar studies on bears in other regions.